Engineers help New York buildings prepare for hurricane season

By Robert L. Reid

WHEN HURRICANE SANDY struck New York City in October 2012, the 34th Street campus of New York University (NYU) Langone Health—a teaching hospital campus of roughly a dozen buildings located along the East River—was flooded by an estimated 15 million gal. of water. Buildings lost power, medical equipment was destroyed, and the facility was closed for months. Determined not to suffer such a disaster again, the medical center—and several other facilities in the region—have been working over the intervening years with the international engineering firm Thornton Tomasetti to prepare for both the immediate threats of the next hurricane season and longer-term hazards, says Amy Macdonald, CFM, an associate principal and the resilience practice leader in Thornton Tomasetti’s New York City office.

“The approach has been not just to look backward at past events but to look forward and consider how climate change will have an impact on flooding and sea-level rise in the future,” Macdonald notes. Efforts at NYU Langone and other New York City properties have focused on “site-specific risk analysis, physical flood-risk reduction measures, [and] emergency management and preparedness,” taking a “risk-informed, future-focused, and holistic approach to the resilience of their facilities,” Macdonald explains.

“After Sandy, we instituted a comprehensive mitigation plan, with robust and redundant systems designed to fortify the campus to be able to withstand a storm well above the 500-year flood level,” said Paul Schwabacher, P.E., NYU Langone’s senior vice president, facilities management. “Our emergency management team has been expanded, and employees train in emergency management throughout the year. Critical infrastructure systems are tested on a regular basis, and workers practice deploying the campus flood barriers.”

For the 2020 hurricane season, temporary and permanent flood barriers have been installed and carefully tested at the medical center’s buildings.

Working incrementally before and during each subsequent hurricane season—which begins June 1 and poses the biggest threat to the New York region from August through the end of November—a team of engineers, architects, and construction professionals has improved and elevated NYU Langone’s emergency power generators. They have been lifted to a level above the current floodplain as well as a predicted future floodplain calculated using climate change projections,
Macdonald notes.

For the 2020 hurricane season, both temporary and permanent flood barriers have been installed and carefully tested at the medical center’s buildings. These barriers include flexible walls made from high-strength textiles that are manually deployed and rigid flip-up barriers that can be activated in one of three ways: manually, by push-button, or automatically, triggered by sensors. These systems protect doors or openings in the floodwalls along the campus perimeter. 

While flood barriers are typically tested by their manufacturers in controlled environments, Thornton Tomasetti recommends that barriers also be tested in place to ensure their construction and their incorporation within any wider flood-mitigation strategy aligns with the design intent, Macdonald explains. The three-part testing of these systems is based on Approval Standard FM2510, from the flood-mitigation products certification organization FM Approvals. Engineers begin with visual observations that look for air gaps along the flood-barrier perimeters and any joints, Macdonald says. Next, they conduct high-pressure hose tests using nozzles that can generate at least 20 psi of water pressure before the tests. The tests focus on any mechanical, hydraulic, or pneumatic seals or gaskets; any overlaps or transitions between barrier components; and any other joints as well as any penetrations, fasteners, or hardware that penetrate the barrier, Macdonald explains.

If a leak is observed, the location is identified and the leakage rate is measured to determine if it is within the flood barrier manufacturer’s specifications, Macdonald advises. The leakage rate can be determined by collecting the water in a container of known dimensions, then measuring the height of water collected once per minute. At least five measurements are collected to determine the leakage volume per minute, Macdonald says.

The third type of test is a so-called bathtub test that measures the water loads against the installed barrier system to locate any deficiencies, explains Macdonald. This is accomplished by erecting a structure, generally made of plywood and timber with a waterproof membrane inside, that is pressed against the floodwall, door, or other barrier and filled with water. Although the exact dimensions of bathtub systems vary by the buildings and specific barriers being tested, they tend to range from a roughly 4 to 5 ft long tub to test a single flood door up to a roughly 35 ft long system to test a much larger barrier, Macdonald says. The tubs are filled up to the barrier-specific design flood elevation to mimic the hydrostatic conditions behind the barrier, she says. 

The tubs are filled up to the barrier-specific design flood elevation to mimic the hydrostatic conditions behind the barrier.

Because of logistical constraints, Thornton Tomasetti did not conduct debris impact tests on any of these projects. But Macdonald says that the manufacturers conduct such tests before they deliver and install the systems.

Other flood-protection projects that Thornton Tomasetti is working on in New York City include the revitalization of the 1.2 million sq ft Terminal Warehouse complex in the West Chelsea neighborhood and a historical city-owned building located along the East River known as the Fireboat House. For the Fireboat House, the firm designed a flood-protection system that will use engineered flood vents—a so-called wet flood-proofing technique. Available only for buildings with no underground levels, the stainless-steel vents measure 16 by 8 in., with one vent required for each 200 sq ft of area. The vents must be located on at least two walls at ground level to allow water to flow freely in and out. This will “minimize the chance of water building up against an exterior wall and resulting in structural damage,” Macdonald explains. Still in the design stage, the Fireboat House’s flood-vent system will be installed later as part of a longer-term flood-resilience strategy, Macdonald says.

Because the physical barrier systems only work as well as they are designed, constructed, installed, and maintained—especially the systems that must be deployed manually—Thornton Tomasetti’s engineers help train clients’ staffs to ensure “all the people involved in deploying hurricane- and flood-mitigation measures are well versed and well practiced and the lines of communication and responsibility are very clear,” Macdonald concludes.

This article first appeared in the September 2020 issue of Civil Engineering.

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